The invention relates to spray pyrolysis, which involves forming a film by spraying onto a heated substrate an atomized solution containing the appropriate salts of the constituent elements of the film compound. The chemical reaction occurs upon spraying on the heated substrate, and the nonconstituent elements of the salts are removed by volatilization along with the solvent, typically water. For example, U.S. Pat. No. 3,148,084 discloses, along with other examples, the formation of CdS by spray pyrolysis, according to the following equation: EQU CdCl.sub.2 +H.sub.2 NC(.dbd.S)NH.sub.2 .fwdarw.CdS+volatile products
Before the conception of the invention, Messrs. Steven A. Lis, Harvey B. Serreze, and Peter M. Sienkiewicz proposed the process claimed in a copending patent application Ser. No. 231,127, filed Feb. 3, 1981 involving placing an agent directly in a spray solution to cause a variety of desirable oxidation/reduction reactions to occur when the spray solution contacted the heated substrate. They tried placing hydrazine and oxalic acid reducing agents in the spray solutions before spraying, and although the desired oxidation/reduction reaction occurred, efforts continued to improve the purity of the product.